Processing units, such as processing cores, central processing units (CPUs), and graphic processing units (GPUs), are designed to operate within a supply voltage range. For example, a processing unit can be designed to operate within a voltage range of a nominal supply voltage, such as 5 volts. The supply voltage range can include a minimum supply voltage where, if the processing unit is supplied with a supply voltage less than the minimum supply voltage, the processing unit becomes unreliable. Processing units are also designed to operate within a temperature range where if the processing unit operates outside of the temperature range, the processing unit can become unreliable. Consequently, a processing unit is typically manufactured at a grade, such as a commercial, industrial, or military grade, where the grade represents a temperature range the processing unit is designed to operate within. For example, while a commercial graded processing unit can be designed to operate within a temperature range of 0 degrees Celsius (C) to 70 degrees C., a military graded processing unit can be designed to operate within a temperature range of −55 degrees C. to 125 degrees C.
A processing unit's dynamic power is directly related to the processing unit's supply voltage and to its operating (e.g., executing) frequency (e.g., speed). The higher a processing unit's supply voltage is, given the same operating frequency of the processor, the higher its dynamic power will be. Similarly, the higher the processing unit's operating frequency is, given the same supply voltage, the higher the processing unit's dynamic power will be. Thus, a processing unit's dynamic power increases or decreases based on its supply voltage and operating frequency.
A processing unit can also leak from the transistors making up the processing unit current causing the processing unit to lose power in the form of leakage power. The temperature a processing unit is operating at, and the supply voltage of the processing unit, are both directly related to a processing unit's leakage power. Typically, the higher a processing unit's operating temperature, given the same supply voltage, the higher the processing unit's leakage power will be. Similarly, the higher a processing unit's supply voltage, assuming the same operating temperature, the higher the processing unit's leakage power will be.
A processing unit's normalized power is based on the processing unit's dynamic power and leakage power compared to the processing unit's dynamic power and leakage power at a reference operating temperature, reference supply voltage, and reference operating frequency. For example, a processing unit's normalized power can be calculated as the addition of processing unit's dynamic power to its leakage power at a supply voltage and operating temperature divided by the addition of the processing unit's dynamic and leakage power at a reference supply voltage and reference operating temperature.
As a result of higher operating temperatures, transistors can undergo an effect known as temperature inversion where a transistor's operating speed becomes faster at the higher operating temperatures. Typically a processing unit's transistors will operate slower as their operating temperature increases. However, in the temperature inversion region of a processing unit's transistors, as the processing unit heats up (resulting in a higher operating temperature) its transistors can begin to operate at a faster rate. In addition, the processing unit's leakage power can increase, at least in part due to the higher operating temperature, thus resulting in processing power and/or speed inefficiencies. The effects of temperature inversion on a processing unit have largely been ignored because temperature inversion does not occur in typical supply voltage ranges of a processing unit. These effects, however, are becoming increasingly relevant in current and future technologies, such as in devices that employ Fin Field Effect Transistors (FinFET), which can operate with lower supply voltages than traditional transistors.
As such, there are opportunities to address temperature inversion effects on a processing unit while operating at lower supply voltages.